stream.filter一般适用于list集合,主要作用就是模拟sql查询，从集合中查询想要的数据。filter里面的参数user是指集合里面的每一项

public class StreamTest{
    public static void main(String[] args){
        List<User> list = new ArrayList<>();
        //定义三个用户对象
        User user1 = new User();
        user1.setUsername("huxiansen");
        user1.setPassword("123456");
        User user2 = new User();
        user2.setUsername("huxianseng");
        user2.setPassword("123456");
        User user3 = new User();
        user3.setUsername("huxiansen");
        user3.setPassword("12345");
        //添加用户到集合中
        list.add(user1);
        list.add(user2);
        list.add(user3);
​
        //在集合中查询用户名为huxiansen的集合
        List<User> userList = list.stream().filter(user -> "huxiansen".equals(user.getUsername())).collect(Collectors.toList());
        //在集合中查询出第一个用户密码为123456的用户
        Optional<User> user = list.stream().filter(userTemp -> "123456".equals(userTemp.getPassword())).findFirst();

    }
}